1. Field of the Invention
This invention relates to a multiple-use thermal image transfer recording method by use of a thermal image transfer recording medium, capable of yielding images with high density, with a minimum decrease in the image density even when it is repeatedly used.
2. Discussion of Background
Recording apparatus, such as a printer and a facsimile apparatus, employing a thermal image transfer recording method, is now widely used. This is because the recording apparatus of this type is relatively small in size and can be produced inexpensively, and the maintenance is simple.
In a conventional thermal image transfer recording medium for use with the thermal image transfer recording apparatus, a single thermal image transfer ink layer is merely formed on a support. When such a recording medium is used for printing images, the ink layer portions heated by a thermal head are completely transferred to an image-receiving sheet at only one-time printing, so that the recording medium can be used only once, and can never be used repeatedly. The conventional recording medium is thus disadvantageous from the viewpoint of running cost.
In order to overcome the above drawback in the prior art, there have been proposed the following methods:
(1) A microporous ink layer containing a thermofusible ink is formed on a support so that the ink can gradually ooze out from the ink layer as disclosed in Japanese Laid-Open Patent Application 55-105579; PA1 (2) A porous film is provided on an ink layer formed on a support so that the amount of an ink which oozes out from the ink layer Can be controlled as disclosed in Japanese Laid-Open Patent Application 58-212993; and PA1 (3) An adhesive layer is interposed between an ink layer and a support so that an ink in the ink layer can be gradually exfoliated in the form of a thin layer from the ink layer when images are printed as disclosed in Japanese Laid-Open Patent Applications 60-127191 and 60-127192.
However, when images are printed on an image-receiving sheet in general use by using the above-mentioned conventional thermal image transfer recording media, there are the shortcomings that the image density of the obtained images is low or considerably decreased during the repeated printing operation.
Many proposals have also been made to eliminate the above drawback from the image-receiving sheet for use in the thermal image transfer recording system.
For instance, image-receiving sheets comprising a support and a coated layer with high oil-absorbability are disclosed in Japanese Laid-Open Patent Applications 57-182487, 61-217289, 61-248791, 61-266296, 61-284488, 62-162590, 62-202788, 62-160287, 62-257888, 62-278082, 63-19289, 63-69685, 63-178082 and 01-188392.
However, even when the aforementioned image-receiving sheets with a high oil-absorbability are used for thermal image transfer recording, images with high resolution and high image density cannot be obtained without reduction in image density during the repeated printing operation.
Japanese Laid-Open Patent Application 02-9688 discloses that an image-receiving sheet with a surface roughness index (Vr) of 5 or more measured in accordance with the Bristow method (J. TAPPI Testing Method for Paper and Pulp No. 51 - 87) provides satisfactory images. When the thermal image transfer recording medium is repeatedly used for printing images on such an image-receiving sheet, however, images with high resolution and high density cannot be maintained for an extended period of time.